Catalysts have been used widely in the refining and chemical processing industries for many years. Hydroprocessing catalysts, including hydrotreating and hydrocracking catalysts, are now widely employed in facilities worldwide. After being used for hydroprocessing, used or “spent” hydroprocessing catalysts typically contain metal components such as molybdenum, nickel, cobalt, vanadium, and the like.
With the advent of heavier crude feedstock, refiners are forced to use more catalysts than before for hydroprocessing and to remove catalyst contaminants and sulfur from the feedstock. These catalytic processes generate quantities of spent catalyst. With the increasing demand and market price for metal values and environmental awareness thereof, catalysts can serve as a source for metal recovery.
In order to recycle catalytic metals and provide a renewable source for the metals, efforts have been made to selectively extract metals from mixtures. It has been reported by Yatirajam et al. of Kurukshetra University, India (1972), among other sources including U.S. Pat. No. 7,255,795, that molybdenum (Mo) can be selectively extracted as molybdenum xanthate from other metal elements, including vanadium, from liquid mixtures by potassium ethyl xanthate at an acidic pH with the use of agents such as hydrochloric acid. US Patent Publication No. 2007/0025899 discloses a process to recover metals such as molybdenum, nickel, and vanadium from a spent catalyst with a plurality of steps and equipment to recover the molybdenum and nickel metal complexes. U.S. Pat. No. 6,180,072 discloses another complex process requiring oxidation steps and solvent extraction to recover metals from spent catalysts containing at least a metal sulphide. U.S. Pat. No. 7,846,404 discloses a process using pH adjustment and precipitation, for recovery of metals from ammoniacal pressure leach solution generated through oxidative pressure leaching of spent catalyst.
There is still a need for improved methods to recover metals including but not limited to molybdenum, nickel, and vanadium from spent catalysts. In one embodiment, the invention relates to a method for recovering Group VIB metals from a pressure leach solution in a process to recover metals from spent catalyst.